Reforming process with improved heater integration

ABSTRACT

A method and apparatus for processing a hydrocarbon stream are described. The method includes heating a feed stream in a convective bank. The heated feed stream is reacted in a first reaction zone to form a first effluent, which is heated in a first radiant cell. The first radiant cell combusts fuel to heat the first effluent and forms a first exhaust gas. The first exhaust gas is contacted with the convective bank to heat the feed stream. The outlet temperature the heated feed stream from the convective bank is controlled by introducing an additional gas stream into the convective bank. There can be additional reaction zones and radiant heaters.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application No.62/336,349 filed May 13, 2016, the contents of which cited applicationare hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Hydrocarbon conversion processes often employ a series of reaction zonesthrough which hydrocarbons pass. Each reaction zone may have its ownunique process requirements, including a required temperature.Accordingly, each reaction zone requires a sufficient amount of heatingupstream of the reaction zone to achieve the required temperature forperforming the desired hydrocarbon conversion therein.

One well-known hydrocarbon conversion process is catalytic reforming.Catalytic reforming is a well-established hydrocarbon conversion processemployed in the petroleum refining industry for improving the octanequality of hydrocarbon feed streams. The primary product of catalyticreforming is a gasoline blending component or a source of aromatics forpetrochemicals. Reforming may be defined as the total effect produced bydehydrogenation of cyclohexanes and dehydroisomerization ofalkylcyclopentanes and high carbon content C₆ to C₇ naphthenes to yieldaromatics, dehydrogenation of paraffins to yield olefins,dehydrocyclization of paraffins and olefins to yield aromatics,isomerization of n-paraffins, isomerization of alkylcycloparaffins toyield cyclohexanes, isomerization of substituted aromatics, andhydrocracking of paraffins. A reforming feed stream can be a productstream from a hydrocracker, a fluid catalytic cracker (FCC), or a coker,or a straight run naphtha feed, and can contain many other componentssuch as a condensate or a thermal cracked naphtha.

Heaters or furnaces are often used in hydrocarbon conversion processes,such as reforming, to heat the process fluid before it is reacted.Generally, fired heaters or furnaces include a radiant fired heatingzone to heat the fluid, with a convective section being used for anotherservice, such as producing steam. Each section includes tubes to containthe process fluid flowing through the heater. The U-tube fired heaterassembly is an expensive mainstay of catalytic reforming. This designcombines several key advantages, including: (a) a low coil pressuredrop, (b) flexibility in duty specifications between cells, (c) abilityto integrate multiple cells with a common heat recovery system, and (d)turndown control that protects downstream plate-type exchanger fromsudden temperature changes.

Typical reforming process designs have developed duty specifications forthe multiple fired heater cells in order to provide the same inlettemperature to each reaction stage.

However, in view of the rising costs of fuel, conventional designssuffer disadvantages. Specifically, the production of steam byconvective sections is non-optimal as steam is provided in other areasof hydrocarbon processing plants. Rather, heat from the fuel combustedin the radiant fired heating zone can be better concentrated on anincrease in enthalpy in hydrocarbon processing.

Accordingly, methods for processing hydrocarbons utilizing convectivesections to heat hydrocarbon streams have been developed. For example,U.S. Pat. No. 9,206,358 describes a method for heating a feed stream ina convective bank. The feed stream is reacted in a first reaction zoneto form a first effluent. The first effluent is heated is a firstradiant cell that combusts fuel gas to heat the first effluent and formsa first exhaust gas. The method include contacting first exhaust gaswith the convective bank to heat the feed stream. However, this processdoes not permit effective temperature control for the charge heaterdischarge temperature, resulting in under-utilization of first reactorprocess yield.

Therefore, there is a need for methods of processing hydrocarbons usingconvective sections to heat hydrocarbon streams which providetemperature control for the charge heater discharge temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of one embodiment of a method and apparatusfor heating a feed stream according to the present invention.

FIG. 2 is an illustration of the flow of exhaust gases and theadditional gases used to control the heated feed stream outlettemperature from the convective bank.

SUMMARY OF THE INVENTION

One aspect of the invention is a method for processing a hydrocarbonstream. In one embodiment, the method includes heating a feed stream ina convective bank. The heated feed stream is reacted in a first reactionzone to form a first effluent, and the first effluent is heated in afirst radiant cell. The first radiant cell combusts fuel to heat thefirst effluent and forms a first exhaust gas. The first exhaust gas iscontacted with the convective bank to heat the feed stream. The outlettemperature the heated feed stream from the convective bank iscontrolled by introducing an additional gas stream into the convectivebank.

Another aspect of the invention is an apparatus for processing ahydrocarbon stream. In one embodiment, the apparatus comprises a heatexchanger configured to heat a feed stream. There is a convective bankconfigured to receive the feed stream and an additional gas stream.There is a reaction zone configured to receive a heated feed stream fromthe convective bank and to react the heated feed stream to form aneffluent. There is a radiant cell configured to receive and heat theeffluent; the radiant cell forms an exhaust gas, and is configured topass a portion of the exhaust gas to the convective bank to heat thefeed stream. A temperature sensor is configured to monitor a temperatureof the heated feed stream exiting the convective bank. There is a flowcontroller configured to change an amount of the portion of the exhaustgas flowing to the convective bank in response to the temperature of theheated feed stream exiting the convective bank.

DETAILED DESCRIPTION OF THE INVENTION

Significant cost and plot space reductions in the heater assembly can beobtained when heater duty requirements are considered within selectingcatalytic inlet temperatures. By providing a lower inlet temperature tothe first reaction stage, the charge heater radiant cell can berelocated into the heat recovery section of the heater assembly. Controlover the inlet temperature of the first reactor is achieved by temperingthe flue gas inlet temperature to the heat recovery system. The overallprocess efficiency is improved, leading to a reduction in the fuelfiring requirements of about 15% to about 30%, and resulting in about a10% to about 25% reduction in the cost of the fired heater assembly.

The invention involves controlling the temperature of the outlet streamfrom the convective bank by introducing an additional gas stream intothe convective bank. The additional stream can be fresh gas, a portionof the exhaust gas from the convective bank, or both. The temperature ofthe additional gas can be controlled; the additional gas can be heatedor cooled if necessary. Alternatively or in addition, the blend of thefresh gas and the exhaust gas can be varied.

Methods and apparatus for processing hydrocarbon streams, and moreparticularly, for heating hydrocarbon streams in convective sectionsupstream of reaction zones are provided. The methods and apparatusreduce fuel costs for radiant fired heating zones, as increased amountsof energy produced from combustion of the fuel is transferred to thehydrocarbon streams through convective sections. The methods andapparatus provide effective temperature control of the inlet temperatureof the first reactor.

As used herein, the phrase “hydrocarbon stream” includes any streamincluding various hydrocarbon molecules, such as straight-chain,branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, andoptionally other substances including gases, such as hydrogen. Thehydrocarbon stream may be subject to reactions, for example, reformingreactions, but still may be referred to as a hydrocarbon stream, as longas at least some hydrocarbons are present in the stream after thereaction. Thus, the hydrocarbon stream may include streams that aresubjected to one or more reactions, e.g., a hydrocarbon stream effluent,or not subjected to any reactions, e.g., a naphtha feed. As used herein,a hydrocarbon stream can also include a raw hydrocarbon feed stream, acombined feed stream, or an effluent.

The methods and apparatus for heating hydrocarbons for processing asdescribed herein are particularly applicable to processes utilizing atleast two reaction zones, where at least a portion of the hydrocarbonstream flows serially through the reaction zones. Processes havingmultiple reaction zones may include a wide variety of hydrocarbonconversion processes such as reforming, hydrogenation, hydrotreating,dehydrogenation, isomerization, dehydroisomerization,dehydrocyclization, cracking, and hydrocracking processes. Catalyticreforming often utilizes multiple reaction zones, and will be referencedhereinafter in the embodiments depicted in the drawings. However, theclaimed methods and apparatus are not limited for catalytic reformingprocesses.

The drawings illustrate an embodiment of a method and apparatus forhydrocarbon processing as applied to a catalytic reforming process. Thedrawings are presented solely for purposes of illustration and are notintended to limit the scope of the claims as set forth below. Thedrawings show only the equipment and lines necessary for anunderstanding of various embodiments herein and do not show equipmentsuch as pumps, compressors, heat exchangers, and valves which are notnecessary for an understanding of the methods and apparatus claimedherein and which are well known to persons of ordinary skill in the artof hydrocarbon processing.

Referring to FIG. 1, an apparatus 10 for processing a hydrocarbon feedstream 12 is schematically depicted. The exemplary apparatus 10 is areforming unit including a heat exchange section 14, a radiant firedheating section 16, a convective heating section 18, a reaction section20, and a product recovery section 22.

As shown, the hydrocarbon feed stream 12 flows to the heat exchangesection 14 upstream of sections 16, 18 and 20. An exemplary hydrocarbonfeed stream 12 for catalytic reforming is a petroleum fraction known asnaphtha, having an initial boiling point of about 82° (about 180° F.)and an end boiling point of about 203° C. (about 400° F.). The catalyticreforming process is particularly applicable to the treatment ofstraight run naphthas comprised of relatively large concentrations ofnaphthenic and substantially straight chain paraffinic hydrocarbons,which are subject to aromatization through dehydrogenation and/orcyclization reactions. Exemplary charge stocks are naphthas consistingprincipally of naphthenes and paraffins that can boil within thegasoline range, although, in many cases, aromatics also can be present.This class of naphthas includes straight-run gasolines, naturalgasolines, synthetic gasolines, and the like. Other embodiments maycharge thermally or catalytically cracked gasolines or partiallyreformed naphthas. Mixtures of straight-run and cracked gasoline-rangenaphthas can also be used to advantage. The gasoline-range naphthacharge stock may be a full-boiling gasoline having an initial boilingpoint of about 40° C. to about 82° C. (about 104° F. to about 180° F.)and an end boiling point within the range of about 160° C. to about 220°C. (about 320° F. to about 428° F.), or may be a selected fractionthereof which generally can be a higher-boiling fraction commonlyreferred to as a heavy naphtha, for example, a naphtha boiling in therange of about 100° C. to about 200° C. (about 212° F. to about 392°F.). In some cases, it is also advantageous to charge pure hydrocarbonsor mixtures of hydrocarbons that have been recovered from extractionunits, for example, raffinates from aromatics extraction orstraight-chain paraffins, which are to be converted to aromatics. Insome other cases, the feed stream 12 may also contain light hydrocarbonsthat have 1-5 carbon atoms, but since these light hydrocarbons cannot bereadily reformed into aromatic hydrocarbons, these light hydrocarbonsentering with the feed stream 12 are generally minimized.

As is typical for catalytic reforming processes, the feed stream 12 isadmixed with a recycled stream 24 comprising hydrogen to form what iscommonly referred to as a combined feed stream 26 before being deliveredto a combined feed heat exchanger 30 in the heat exchange section 14.Generally, the recycled stream 24 supplies hydrogen in an amount ofabout 1 to about 20 moles of hydrogen per mole of hydrocarbon feedstream 12. For example, hydrogen may be supplied to provide an amount ofless than about 3.5 moles of hydrogen per mole of hydrocarbon feedstream 12. If hydrogen is supplied, it may be supplied upstream of thecombined feed heat exchanger 30, downstream of the combined feed heatexchanger 30, or both upstream and downstream of the combined feed heatexchanger 30. Alternatively, no hydrogen may be supplied. Even ifhydrogen is not provided to the hydrocarbon feed stream 12, naphthenereforming reactions that occur within the reaction section 20 can yieldhydrogen as a by-product. This by-product, or in-situ-produced, hydrogencan become available as hydrogen downstream reaction zones within thereaction section 20. In situ hydrogen in the reaction section 20 maytotal from about 0.5 to about 2 moles of hydrogen per mole ofhydrocarbon feed stream 12.

In the combined feed heat exchanger 30, the combined feed stream 26 canbe heated by exchanging heat with the product effluent 36 of thereaction section 20. However, the heating of the combined feed stream 26that occurs in the combined feed heat exchanger 30 is generallyinsufficient to heat the combined feed stream 26 to the desired inlettemperature of the reaction section 20. In a typical catalytic reformingprocess, the combined feed stream 26, or the hydrocarbon feed stream 12if no hydrogen is provided with the hydrocarbon feed stream 12, entersthe combined feed heat exchanger 30 at a temperature of generally about38° C. to about 177° C. (about 100° F. to about 350° F.), and moreusually about 93° C. to about 121° C. (about 200° F. to about 250° F.).Generally, the combined feed heat exchanger 30 heats the combined feedstream 26 by transferring heat from the product effluent 36 of the lastreforming reaction zone in the reaction section 20 to the combined feedstream 26. An exemplary combined feed heat exchanger 30 is an indirect,rather than a direct, heat exchanger, in order to prevent valuablereformate product in the product effluent 36 from intermixing with thecombined feed stream 26, and thereby being recycled to the reactionsection 20, where the reformate quality could be degraded.

In an exemplary embodiment, the flow pattern of the combined feed stream26 and the product effluent 36 within the combined feed heat exchanger30 is countercurrent, through it could be completely co-current,reversed, mixed, or cross flow. In a countercurrent flow pattern, thecombined feed stream 26, while at its coldest temperature, contacts oneend (i.e., the cold end) of the heat exchange surface of the combinedfeed heat exchanger 30 while the product effluent 36 contacts the coldend of the heat exchange surface at its coldest temperature as well.Thus, the product effluent 36, while at its coldest temperature withinthe heat exchanger, exchanges heat with the combined feed stream that isalso at its coldest temperature within the heat exchanger. At anotherend (i.e., the hot end) of the combined feed heat exchanger surface, theproduct effluent 36 and the combined feed stream, both at their hottesttemperatures within the heat exchanger, contact the hot end of the heatexchange surface and thereby exchange heat. Between the cold and hotends of the heat exchange surface, the product effluent 36 and thecombined feed stream flow in generally opposite directions, so that, ingeneral, at any point along the heat transfer surface, the hotter thetemperature of the product effluent 36, the hotter is the temperature ofthe combined feed stream with which the product effluent 36 exchangesheat. The exemplary combined feed heat exchanger 30 operates with a hotend approach that is generally less than about 56° C. (about 100° F.),such as less than about 33° C. (about 60° F.), for example, less thanabout 28° C. (about 50° F.).

Although the combined feed heat exchanger 30 may utilize shell-and-tubetype heat exchangers, it may alternatively use plate type heatexchangers. Plate type exchangers are well known and commerciallyavailable in several different and distinct forms, such as spiral, plateand frame, brazed-plate fin, and plate fin-and-tube types.

In one embodiment, the combined feed stream 26 leaves the combined feedheat exchanger 30 as a heated feed stream 40 at a temperature of about399° C. to about 516° C. (about 750° F. to about 960° F.). Because thereforming reactions that occur first in the reaction zone 60 take placeat an elevated temperature and are generally endothermic, the heatedfeed stream 40 often requires additional heating after exiting thecombined feed heat exchanger 30 and prior to entering the reactionsection 20.

In prior art apparatus, this additional heating is provided in a radiantcell such as a charge heater, for example, a gas-fired, oil-fired, ormixed gas-and-oil-fired heater, that heats the heated feed stream 40 byradiant or radiant and convective heat transfer. The heated feed stream40 bypasses the radiant heating zone(s) and instead is heated in theconvective heating section 18 without passing through a radiant heater.

In the convective heating section 18, the heated feed stream 40 flowsthrough a convective heat bank 50 as described further in relation toFIG. 2 below. The heated feed stream 40 is typically heated to atemperature of about 427° C. to about 649° C. (about 800° F. to about1,200° F.), or about 482° C. to about 593° C. (about 900° F. to about1,100° F.), or about 510° C. to about 566° C. (about 950° F. to about1,050° F.). As shown, the convectively heated stream 54 exits theconvective heating section 18 and flows to the reaction section 20.

In some embodiments, the flue gas 51 (at a temperature of about 732° C.to about 899° C. (about 1350° F. to about 1650° F.)) flows from theconvective heat bank 50 to a steam convection bank 52 where the flue gasis used to produce steam. The flue gas 53 exits the steam convectionbank 52 at a temperature of about 149° C. to about 260° C. (about 300°F. to about 500° F.), and at least a portion 55 of the flue gas 53 isrecycled to the convective heat bank 50. The recycled flue gas portion55 may be compressed before being introduced into the convective heatbank 50. In other embodiments, the flue gas could be used in other heatrecovery processes, or it could be recycled to the convective heat bank50 without any additional heat recovery.

Alternatively, or in addition, a fresh gas stream 56 is introduced intothe convective heat bank 50. The fresh gas stream 56 can be heated orcooled as needed, and it may also be compressed if desired. The inlettemperature for the fresh gas stream 56 can be about−12° C. to about982° C. (about 10° F. to about 1800° F.)). Suitable gases include, butare not limited to, air, nitrogen, or another flue gas stream.

A temperature indicator/controller 58 is in communication with theconvectively heated stream 54 upstream of the reaction section 20. Thetemperature indicator/controller 58 monitors the temperature of theconvectively heated stream 54. When the temperature exceeds apredetermined maximum temperature, such as about 566° C. (1050° F.), orfalls below a predetermined minimum temperature, such as about 510° C.(950° F.), the temperature indicator/controller 58 adjusts the amount ofthe recycled flue gas portion 55 and/or the amount and temperature ofthe fresh gas stream 56 entering the convective heat bank 50.

As shown, the convectively heated stream 54 enters the exemplaryreaction section 20 which includes four reaction zones 60 through whichhydrocarbons flow serially. Reaction sections having multiple reactionzones 60 generally take one of two forms: a stacked form as shown inFIG. 1 or a side-by-side form. In the side-by-side form, multiple andseparate reaction vessels, each that can include a reaction zone, may beplaced beside each other. In the stacked form, one common reactionvessel 62 contains multiple and separate reaction zones 60 that areplaced on top of each other. In either arrangement, there can beintermediate heating or cooling between the reaction zones 60, dependingon whether the reactions are endothermic or exothermic.

The exemplary catalytic reforming process utilizes a reaction section 20with a first reaction zone 71, a second reaction zone 72, a thirdreaction zone 73, and a fourth reaction zone 74. There may be any numberof reaction zones 60, but usually the number of reaction zones 60 isthree, four or five. Hydrocarbons undergo conversion reactions in eachreaction zone 60, in the presence of catalyst particles 76. Theexemplary reforming process employs catalyst particles 76 in thereaction zones 60 in a series flow arrangement, and spent catalystparticles 78 may exit the reaction section 20 as shown.

In overview, the first reaction zone 71 receives the convectively heatedstream 54 as a first reactor feed and produces a first reactor effluent81. Endothermic reforming reactions that occur in the first reactionzone 71 generally cause the outlet temperature of the first reactionzone 71 to fall not only to less than the temperature of theconvectively heated stream 54, but also to less than the desired inlettemperature of the second reaction zone 72. Therefore, the first reactoreffluent 81 is heated in the radiant fired heating section 16 to thedesired inlet temperature of the second reaction zone 72 as discussedbelow and is returned to the reaction section 20 as second reactor feed82. The second reaction zone 72 reacts the second reactor feed 82 toform a second reactor effluent 83. Again, due to endothermic reactions,the second reactor effluent 83 requires heating to reach the desiredinlet temperature of the third reaction zone 73. The second reactoreffluent 83 flows to and is heated by the radiant fired heating section16 as discussed below and is returned to the reaction section 20 as athird reactor feed 84. The third reaction zone 73 reacts the thirdreactor feed 84 to form a third reactor effluent 85. As above,endothermic reactions may cause the temperature of the third reactoreffluent 85 to fall below the desired inlet temperature of the fourthreaction zone 74. The third reactor effluent 85 flows to and is heatedby the radiant fired heating section 16 as discussed below and isreturned to the reaction section 20 as a fourth reactor feed 86. Thefourth reaction zone 74 reacts the fourth reactor feed 86 to form theproduct effluent 36.

Exemplary reaction zones 60 can be operated at reforming conditions,which include a range of pressures generally from atmospheric pressureof about 0 kPa(g) to about 6,895 kPa(g) (about 0 psig to about 1,000psig), with particularly good results obtained at the relatively lowpressure range of about 276 kPa(g) to about 1,379 kPa(g) (about 40 psigto about 200 psig). The overall liquid hourly space velocity (LHSV)based on the total catalyst volume in all of the reaction zones isgenerally about 0.1 hr⁻¹ to about 10 hr⁻¹, such as about 1 hr⁻¹ to about5 hr⁻¹, for example, about 1.5 hr⁻¹ to about 2.0 hr⁻¹.

Generally naphthene reforming reactions that are endothermic occur inthe first reaction zone 71, and thus the outlet temperature of the firstreaction zone 71 can be less than the inlet temperature of the firstreaction zone 71 and is generally about 316° C. to about 454° C. (about600° F. to about 850° F.). The first reaction zone 71 may containgenerally about 5% to about 50%, and more usually about 10% to about30%, of the total catalyst volume in all of the reaction zones 60.Consequently, the liquid hourly space velocity (LHSV) in the firstreaction zone 71, based on the catalyst volume in the first reactionzone 71, can be generally 0.2-200 hr⁻¹, such as about 2 hr⁻¹ to about100 hr⁻¹, for example about 5 hr⁻¹ to about 20 hr⁻¹. Generally, thecatalyst particles are withdrawn from the first reaction zone 71 andpassed to the second reaction zone 72. The particles generally have acoke content of less than about 2 wt % based on the weight of catalyst.

An exemplary catalytic conversion process includes catalyst particles 76that are movable through the reaction zones 60. The catalyst particles76 may be movable through the reaction zones 60 by any number of motivedevices, including conveyors or transport fluid, but most commonly thecatalyst particles 76 are movable through the reaction zones 60 bygravity. Catalyst particles 76 can be withdrawn from a bottom portion ofan upper reaction zone and introduced into a top portion of a lowerreaction zone. The spent catalyst particles 78 withdrawn from the finalreaction zone can subsequently be recovered from the process,regenerated in a regeneration zone (not shown) of the process, ortransferred to another reaction zone 60. Likewise, the catalystparticles 76 added to a reaction zone can be catalyst that is beingnewly added to the process, catalyst that has been regenerated in aregeneration zone within the process, or catalyst that is transferredfrom another reaction zone 60.

Exemplary reforming reactions are normally effected in the presence ofcatalyst particles 76 comprised of one or more Group VIII (IUPAC 8-10)noble metals (e.g., platinum, iridium, rhodium, and palladium) and ahalogen combined with a porous carrier, such as a refractory inorganicoxide. Although the catalyst may contain about 0.05 to about 2.0 wt % ofGroup VIII metal, a less expensive catalyst, such as a catalystcontaining about 0.05 to about 0.5 wt % of Group VIII metal may be used.An exemplary noble metal is platinum. In addition, the catalyst maycontain indium and/or a lanthanide series metal such as cerium. Thecatalyst particles 76 may also contain about 0.05 to about 0.5 wt % ofone or more Group IVA (IUPAC 14) metals (e.g., tin, germanium, andlead). An exemplary halogen is chlorine and an exemplary carrier isalumina. Exemplary alumina materials are gamma, eta, and theta alumina,with gamma and eta alumina generally being used in selected embodiments.

A reforming process can employ a fixed catalyst bed, or a moving bedreaction vessel and a moving bed regeneration vessel. In the latter,generally regenerated catalyst particles 76 are fed to the reactionvessel 62, typically including several reaction zones 60, and thecatalyst particles 76 flow through the reaction vessel 62 by gravity.During the course of a reforming reaction with a moving catalyst bed,catalyst particles become deactivated as a result of mechanisms such asthe deposition of coke on the particles; that is, after a period of timein use, the ability of catalyst particles to promote reforming reactionsdecreases to the point that the catalyst is no longer useful. Thecatalyst can be reconditioned, or regenerated, before it is reused in areforming process.

Specifically, catalyst may be withdrawn from the bottom of the reactionvessel 62 and transported to a regeneration vessel. In the regenerationvessel, a multi-step regeneration process is typically used toregenerate the catalyst to restore its full ability to promote reformingreactions. Catalyst can flow by gravity through the various regenerationsteps and then be withdrawn from the regeneration vessel and transportedto the reaction vessel 62. Generally, arrangements are provided foradding fresh catalyst as make-up to and for withdrawing spent catalystparticles 78 from the process. Movement of catalyst through the reactionand regeneration vessels is often referred to as continuous though, inpractice, it is semi-continuous. In semi-continuous movement, relativelysmall amounts of catalyst are repeatedly transferred at closely spacedintervals. For example, one batch every twenty minutes may be withdrawnfrom the bottom of the reaction vessel 62 and withdrawal may take fiveminutes, that is, catalyst can flow for five minutes. If the catalystinventory in a vessel is relatively large in comparison with this batchsize, the catalyst bed in the vessel may be considered to becontinuously moving. A moving bed system can have the advantage ofmaintaining production while the catalyst is removed or replaced.Typically, the rate of catalyst movement through the catalyst beds mayrange from as little as about 45.5 kg (about 100 pounds) per hour toabout 2,722 kg (about 6,000 pounds) per hour, or more.

As shown in FIG. 1, downstream of the first reaction zone 71,hydrocarbons flow between the reaction zones 60 and radiant cells 90 inthe radiant fired heating section 16. For example, the first reactoreffluent 81 exits the reaction section 20 and flows into a first radiantcell 91 where it is heated and forms the second reactor feed 82. Thesecond reactor effluent 83 exits the reaction section 20 and flows intoa second radiant cell 92 where it is heated and forms the third reactorfeed 84. Likewise, the third reactor effluent 85 exits the reactionsection 20 and flows into a third radiant cell 93 where it is heated andforms the fourth reactor feed 86.

Effluent flow between reaction zones and radiant cells may typicallyoccur with a flat temperature profile on the reaction zone inlets, i.e.,heated effluent is the same temperature at all reaction zone inlets.Alternately, effluent flow may be managed with a graduated temperatureprofile. In either case, each radiant cell 90 (typically referred to asan interheater when it is located between two reaction zones 60) isheated by combustion of a fuel gas 94, selectively delivered to theradiant cell 90 by a valve 95 to heat the respective effluent to a sametemperature.

As in the first reaction zone 71, endothermic reactions can causeanother decline in temperature across the second reaction zone 72.Generally, however, the temperature decline across the second reactionzone 72 is less than the temperature decline across the first reactionzone 71, because the reactions that occur in the second reaction zone 72are generally less endothermic than the reactions that occur in thefirst reaction zone 71. Despite the somewhat lower temperature declineacross the second reaction zone 72, the second reactor effluent 83 isnevertheless still at a temperature that is less than the desired inlettemperature of the third reaction zone 73. Thus, the second effluent isheated in the second radiant cell 92 to form the third reactor feed 84.

The second reaction zone 72 generally includes about 10% to about 60%,and more usually about 15% to about 40%, of the total catalyst volume inall of the reaction zones 60. Consequently, the liquid hourly spacevelocity (LHSV) in the second reaction zone 72, based on the catalystvolume in the second reaction zone, is generally about 0.13 hr⁻¹ toabout 134 hr⁻¹, such as about 1.3 hr⁻¹ to about 67 hr⁻¹, for exampleabout 3.3 hr⁻¹ to about 13.4 hr⁻¹.

In the third reaction zone 73, endothermic reactions can cause anotherdecline in temperature, though it is typically less than the temperaturedecline across the first reaction zone 71 as the reactions in the thirdreaction zone 73 are generally less endothermic. The third reaction zone73 contains generally about 25% to about 75%, and more usually about 30%to about 50%, of the total catalyst volume in all of the reaction zones60. In order to raise the temperature of the third reactor effluent 85,it is heated in the third radiant cell 93.

In an exemplary embodiment, each reactor effluent 81, 83, and 85 entersand exits the top portion of each radiant cell 91, 92, and 93 throughU-shaped tubes. Alternatively, each reactor effluent 81, 83, 85 mayenter and exit a lower portion of each radiant cell through invertedU-shaped tubes, or enter the top portion where the temperature is lowestin a radiant cell and exit at the bottom where the temperature ishottest in the radiant cell, or conversely, enter at the bottom and exitat the top. Of course, while U-shaped tubes are illustrated, there aremany radiant cell coil configurations or layouts that can be utilizedfor radiant heating of the effluent.

After heating in the third radiant cell 93, the fourth reactor feed 86is delivered to the fourth reaction zone 74. The fourth reaction zone 74contains generally about 30% to about 80%, and more usually about 40% toabout 50%, of the total catalyst volume in all of the reaction zones 60.The inlet temperatures of the third, fourth, and subsequent reactionzones are generally about 482° C. to about 560° C. (about 900° F. toabout 1,040° F.), such as about 493° C. to about 549° C. (about 920° F.to about 1,020° F.).

Because the reforming reactions that occur in the second and subsequent(i.e., third and fourth) reaction zones 60 are generally lessendothermic than those that occur in the first reaction zone 71, thetemperature drop that occurs in the later reaction zones 60 is generallyless than that that occurs in the first reaction zone 71. Thus, theoutlet temperature of the last reaction zone 74 may be about 11° C.(about 20° F.) or less below the inlet temperature of the last reactionzone 74, and indeed may conceivably be higher than the inlet temperatureof the last reaction zone 74. Moreover, any inlet temperature profilescan be utilized with the above-described reaction zones 60. The inlettemperature profiles can be flat or skewed, such as ascending,descending, hill-shaped, or valley-shaped. Desirably, the inlettemperature profile of the reaction zones 60 is flat.

As shown, the product effluent 36 is cooled in the combined feed heatexchanger 30 by transferring heat to the combined feed stream 26. Afterleaving the combined feed heat exchanger 30, the cooled product effluent96 passes to the product recovery section 22. Suitable product recoverysections 22 are well-known. The exemplary product recovery section 22may include a gas-liquid separator for separating hydrogen and C₁-C₃hydrocarbon gases from the product effluent 36, and fractionationcolumns for separating at least a portion of the C₄-C₅ lighthydrocarbons from the remainder of the reformate. In addition, thereformate may be separated by distillation into a light reformatefraction and a heavy reformate fraction. As a result of product recoveryprocesses, a product stream 98 is formed, or multiple product streams 98are formed, containing desired species.

Referring now to FIG. 2, heat transfer between the radiant fired heatingsection 16 and the convective heating section 18 is explained. As shown,each radiant cell 91, 92, 93 includes a radiant tube 102 having an inlet104 and an outlet 106, and may be somewhat U-shaped and orientatedupwardly. Although only one radiant tube is illustrated for each radiantcell 91, 92, 93, it should be understood that generally each radiantcell 91, 92, 93 can include an inlet manifold, a series of tubes, and anoutlet manifold. A series of radiant tubes 102 may be configured in aparallel configuration and can be stacked front-to-back. The radiantcells 91, 92, 93 can be separated by firewalls 112 and include,respectively, at least one burner 122.

As effluent streams pass through each respective radiant cell 90, fuelgas 94 is combusted in the burner 122 and forms flue gas 130A-C. Theflue gas 130A-C rising from the radiant cells 91, 92, 93 can enter theconvective heat bank 50 in the convective heating section 18 through aninlet or inlets 132 and exit through a stack 134. The convective heatbank 50 generally includes several convective tubes 138 in a parallelconfiguration. Each convective tube 138 has an inlet 142 and an outlet144 and can be somewhat U-shaped and oriented sideways. For a pluralityof convective tubes 138, convective tubes 138 can be stackedfront-to-back in rows. Although convective tubes 138 can be orientedbeside one another, it should be understood that other orientations arepossible, such as orienting the U-shaped tubes flat and stacking severalconvective tubes 138 vertically in rows.

The heated feed stream 40 entering the convective heating section 18enters the inlet 142 of the convective tube 138 and is convectivelyheated by thermal transfer from the flue gas 130A-C through theconvective tube 138. While the inlet 142 is indicated as being above theoutlet 144 such that the heated feed stream 40 enters the top portionwhere the temperature is lowest in the convective heating section 18 andexits at the bottom where the temperature is hottest in the convectiveheating section 18 through the sideways-oriented U-shaped convectivetubes 138, other configurations are contemplated. For example, theheated feed stream 40 may enter and exit the top or lower portion of theconvective heat bank 50, or enter at the bottom and exit at the top.

The recycled flue gas portion 55 and/or the fresh gas stream 56 are usedto control the temperature of the convectively heated stream 54. Byadjusting (increasing or decreasing) the temperature or the amount orboth of recycled flue gas portion 55 and/or the fresh gas stream 56, thetemperature of the convectively heated stream 54 can be controlled. Therecycled flue gas portion 55 and/or the fresh gas stream 56 may beintroduced into the convective heat bank 50 separately, or they can becombined first, if desired. They can be introduced directly into theconvective heat bank 50, if desired. Alternatively, or in addition,either or both can be introduced into the flue gas 130A-C between theradiant cell 91, 92, 93 outlet and the inlet to the convective heat bank50 in one or more of the radiant cells 91, 92, 93.

As used herein, the term about means within 10% of the value, or within5%, or within 1%.

As described herein, an apparatus and method for heating a hydrocarbonstream for processing have been provided. In exemplary embodiments, anapparatus and method have been described for catalytic reformingprocesses, though any suitable apparatus and methods for processinghydrocarbons may utilize the heating process discloses herein. Althoughthe embodiments discussed above can be designed for a new hydrocarbonprocessing apparatus, it should be understood that the disclosedfeatures can implemented during the revamp of an existing apparatus.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theclaimed subject matter in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment or embodiments. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope set forth in the appended claims.

SPECIFIC EMBODIMENTS

While the following is described in conjunction with specificembodiments, it will be understood that this description is intended toillustrate and not limit the scope of the preceding description and theappended claims.

A first embodiment of the invention is a method for processing ahydrocarbon stream, the method comprising heating a feed stream in aconvective bank; reacting the heated feed stream in a first reactionzone to form a first effluent; heating the first effluent in a firstradiant cell, wherein the first radiant cell combusts fuel to heat thefirst effluent and forms a first exhaust gas; contacting the firstexhaust gas with the convective bank to heat the feed stream; andcontrolling an outlet temperature of the heated feed stream from theconvective bank by introducing an additional gas stream into theconvective bank. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph wherein the additional gas stream comprises a fresh gas,a recycled portion of the first exhaust gas, or a combination thereof.An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the first embodiment in this paragraphwhere the additional gas stream comprises the fresh gas, and wherein atemperature of the fresh gas or an amount of the fresh gas, or both isadjusted based on the outlet temperature of the heated feed stream. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph whereinthe temperature of the fresh gas is increased. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph where the additional gasstream comprises the fresh gas, and wherein a temperature of the freshgas is in a range of about−12° C. to about 982° C. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph where the additional gasstream comprises the fresh gas, and wherein the fresh gas is compressed.An embodiment of the invention is one, any or all of prior embodimentsin this paragraph up through the first embodiment in this paragraphwhere the additional gas stream comprises the recycled portion of thefirst exhaust gas, and wherein the recycled portion of the first exhaustgas is compressed before being introduced into the convective bank. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph wherethe additional gas stream comprises the recycled portion of the firstexhaust gas, and wherein a temperature of the recycled portion of thefirst exhaust gas is in a range of about 149° C. to about 260° C. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the first embodiment in this paragraph wherethe additional gas stream comprises the recycled portion of the firstexhaust gas, and wherein a temperature of the recycled portion of thefirst exhaust gas or an amount of the recycled portion of the firstexhaust gas, or both is adjusted based on the outlet temperature of theheated feed stream. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph wherein controlling the outlet temperature of the heatedfeed stream from the convective bank comprises monitoring the outlettemperature of the heated feed stream; and adjusting an amount of theadditional gas stream introduced into the convective bank, or adjustinga temperature of the additional gas stream introduced into theconvective bank, or both based on the outlet temperature of the heatedfeed stream. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the first embodiment in thisparagraph wherein a temperature of the additional gas stream is in arange of about 149° C. to about 260° C. An embodiment of the inventionis one, any or all of prior embodiments in this paragraph up through thefirst embodiment in this paragraph further comprising reacting theheated first effluent in a second reaction zone to form a secondeffluent; heating the second effluent in a second radiant cell, whereinthe second radiant cell combusts fuel to radiantly heat the secondeffluent and the combusted fuel forms a second exhaust gas; contactingthe second exhaust gas with the convective bank to heat the feed stream;reacting the heated second effluent in a third reaction zone to form athird effluent; heating the third effluent in a third radiant cell,wherein the third radiant cell combusts fuel to radiantly heat the thirdeffluent and the combusted fuel forms a third exhaust gas; contactingthe third exhaust gas with the convective bank to heat the feed stream;and reacting the heated third effluent in a fourth reaction zone to forma product effluent. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the first embodiment inthis paragraph further comprising passing the product effluent through aheat exchanger; and heating the feed stream in the heat exchanger beforeheating the feed stream in the convective bank. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph further comprisingcondensing the product effluent to form a product stream. An embodimentof the invention is one, any or all of prior embodiments in thisparagraph up through the first embodiment in this paragraph furthercomprising adding a gas stream comprising hydrogen to the feed streambefore heating the feed stream in the convective bank.

A second embodiment of the invention is a method for processing ahydrocarbon stream, the method comprising heating a feed stream in aconvective bank; reacting the heated feed stream in a first reactionzone to form a first effluent; heating the first effluent in a firstradiant cell, wherein the first radiant cell combusts fuel to heat thefirst effluent and forms a first exhaust gas; contacting the firstexhaust gas with the convective bank to heat the feed stream; monitoringan outlet temperature of the heated feed stream from the convectivebank; and controlling the outlet temperature of the heated feed streamby introducing an additional gas stream into the convective bank,wherein the additional gas stream comprises a fresh gas, a recycledportion of the first exhaust gas, or a combination thereof. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the second embodiment in this paragraphwherein the additional gas stream comprises the fresh gas, and wherein atemperature of the fresh gas or an amount of the fresh gas, or both isadjusted based on the outlet temperature of the heated feed stream; orwhere the additional gas stream comprises the recycled portion of thefirst exhaust gas, and wherein the recycled portion of the first exhaustgas or an amount of the recycled portion of the first exhaust gas, orboth is adjusted based on the outlet temperature of the heated feedstream. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the second embodiment in thisparagraph further comprising reacting the heated first effluent in asecond reaction zone to form a second effluent; heating the secondeffluent in a second radiant cell, wherein the second radiant cellcombusts fuel to radiantly heat the second effluent and the combustedfuel forms a second exhaust gas; contacting the second exhaust gas withthe convective bank to heat the feed stream; reacting the secondeffluent in a third reaction zone to form a third effluent; heating thethird effluent in a third radiant cell, wherein the third radiant cellcombusts fuel to heat the third effluent and the combusted fuel forms athird exhaust gas; contacting the third exhaust gas with the convectivebank to heat the feed stream; and reacting the third effluent in afourth reaction zone to form a product effluent. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the second embodiment in this paragraph further comprisingpassing the product effluent through a heat exchanger; and heating thefeed stream in the heat exchanger before heating the feed stream in theconvective bank.

A third embodiment of the invention is an apparatus for processing ahydrocarbon stream, the apparatus comprising a heat exchanger configuredto heat a feed stream; a convective bank configured to receive theheated feed stream and an additional gas stream; a reaction zoneconfigured to receive a heated feed stream from the convective bank andto react the heated feed stream to form an effluent; a radiant cellconfigured to receive and heat the effluent, wherein the radiant cellforms an exhaust gas, and wherein the radiant cell is configured to passa portion of the exhaust gas to the convective bank to heat the feedstream; a temperature sensor configured to monitor a temperature of theheated feed stream exiting the convective bank; and a flow controllerconfigured to change an amount of the additional gas flowing to theconvective bank in response to the temperature of the heated feed streamexiting the convective bank.

Without further elaboration, it is believed that using the precedingdescription that one skilled in the art can utilize the presentinvention to its fullest extent and easily ascertain the essentialcharacteristics of this invention, without departing from the spirit andscope thereof, to make various changes and modifications of theinvention and to adapt it to various usages and conditions. Thepreceding preferred specific embodiments are, therefore, to be construedas merely illustrative, and not limiting the remainder of the disclosurein any way whatsoever, and that it is intended to cover variousmodifications and equivalent arrangements included within the scope ofthe appended claims.

In the foregoing, all temperatures are set forth in degrees Celsius and,all parts and percentages are by weight, unless otherwise indicated.

The invention claimed is:
 1. A method for processing a hydrocarbonstream in a reformer, the method comprising: heating a naphtha feedstream in a convective bank, the convective bank in fluid and thermalcommunication with at least one radiant cell, wherein the entire naphthafeed stream is heated in the convective bank without passing through theat least one radiant cell or another radiant heater before reaching theconvective bank; reacting the heated naphtha feed stream in a firstreformer reaction zone to form a first reformer effluent; heating thefirst reformer effluent in a first radiant cell, wherein the firstradiant cell combusts fuel to heat the first reformer effluent and formsa first flue gas; introducing the first flue gas from the first radiantcell into the convective bank to heat the naphtha feed stream; removingan exhaust gas from the convective bank at a temperature in a range ofabout 732° C. to about 899° C.; and controlling an outlet temperature ofthe heated naphtha feed stream from the convective bank to a temperaturein a range of about 427° C. to about 649° C. by introducing anadditional gas stream into the convective bank so that the additionalgas stream mixes with the flue gas to maintain a temperature in theconvective bank in a range of about 732° C. to about 899° C., whereinthe additional gas stream comprises a fresh gas at a temperature in arange of −12° C. to about 982° C., a recycled portion of the exhaust gasat a temperature in a range of about 149° C. to about 260° C., or acombination thereof, and wherein the fresh gas does not comprise steam.2. The method of claim 1 where the additional gas stream comprises thefresh gas, and wherein a temperature of the fresh gas or an amount ofthe fresh gas, or both is adjusted based on the outlet temperature ofthe heated feed stream.
 3. The method of claim 2 wherein the temperatureof the fresh gas is increased.
 4. The method of claim 1 where theadditional gas stream comprises the fresh gas.
 5. The method of claim 1where the additional gas stream comprises the fresh gas, and wherein thefresh gas is compressed.
 6. The method of claim 1 where the additionalgas stream comprises the recycled portion of the exhaust gas, andwherein the recycled portion of the exhaust gas is compressed beforebeing introduced into the convective bank.
 7. The method of claim 1where the additional gas stream comprises the recycled portion of theexhaust gas.
 8. The method of claim 1 where the additional gas streamcomprises the recycled portion of the exhaust gas, and wherein atemperature of the recycled portion of the exhaust gas or an amount ofthe recycled portion of the exhaust gas, or both is adjusted based onthe outlet temperature of the heated naphtha feed stream.
 9. The methodof claim 1 wherein controlling the outlet temperature of the heated feedstream from the convective bank comprises: monitoring the outlettemperature of the heated naphtha feed stream; and adjusting an amountof the additional gas stream introduced into the convective bank, oradjusting a temperature of the additional gas stream introduced into theconvective bank, or both based on the outlet temperature of the heatednaphtha feed stream.
 10. The method of claim 1 further comprising:reacting the heated first reformer effluent in a second reformerreaction zone to form a second reformer effluent; heating the secondreformer effluent in a second radiant cell, wherein the second radiantcell combusts fuel to radiantly heat the second reformer effluent andthe combusted fuel forms a second flue gas; introducing the second fluegas from the second radiant cell into the convective bank so that thesecond flue gas mixes with the flue gas to heat the naphtha feed stream;reacting the heated second reformer effluent in a third reformerreaction zone to form a third reformer effluent; heating the thirdreformer effluent in a third radiant cell, wherein the third radiantcell combusts fuel to radiantly heat the third reformer effluent and thecombusted fuel forms a third flue gas; introducing the third flue gasfrom the third radiant cell into the convective bank so that the thirdflue gas mixes with the flue gas to heat the naphtha feed stream; andreacting the heated third reformer effluent in a fourth reformerreaction zone to form a product effluent.
 11. The method of claim 10further comprising: passing the naphtha feed stream and the producteffluent through a heat exchanger before heating the naphtha feed streamin the convective bank to preheat the naphtha feed stream.
 12. Themethod of claim 10 further comprising condensing the product effluent toform a product stream.
 13. The method of claim 1 further comprisingadding a gas stream comprising hydrogen to the naphtha feed streambefore heating the naphtha feed stream in the convective bank.
 14. Amethod for processing a hydrocarbon stream in a reformer, the methodcomprising: heating a naphtha feed stream in a convective bank, theconvective bank in fluid and thermal communication with at least oneradiant cell, wherein the entire naphtha feed stream is heated in theconvective bank without passing through the at least one radiant cell oranother radiant heater before reaching the convective bank; reacting theheated naphtha feed stream in a first reformer reaction zone to form afirst reformer effluent; heating the first reformer effluent in a firstradiant cell, wherein the first radiant cell combusts fuel to heat thefirst reformer effluent and forms a first flue gas; introducing thefirst flue gas from the first radiant cell into the convective bank toheat the naphtha feed stream; removing an exhaust gas from theconvective bank, the exhaust gas having a temperature in a range ofabout 732° C. to about 899° C.; monitoring an outlet temperature of theheated naphtha feed stream from the convective bank; and controlling theoutlet temperature of the heated naphtha feed stream to a temperature ina range of about 427° C. to about 649° C. by introducing an additionalgas stream into the convective bank so that the additional gas streammixes with the first flue gas, and adjusting an amount of the additionalgas, or adjusting a temperature of the additional gas, or both inresponse to the outlet temperature of the heated naphtha stream tomaintain a temperature in the convective bank in a range of about 732°C. to about 899° C., wherein the additional gas stream comprises a freshgas, a recycled portion of the exhaust gas, or a combination thereof,wherein the fresh gas is at a temperature in a range of −12° C. to about982° C., and wherein the recycled portion of the first exhaust gas is ata temperature in a range of about 149° C. to about 260° C., and whereinthe fresh gas does not comprise steam.
 15. The method of claim 14wherein the additional gas stream is compressed.
 16. The method of claim14 further comprising: reacting the heated first reformer effluent in asecond reformer reaction zone to form a second reformer effluent;heating the second reformer effluent in a second radiant cell, whereinthe second radiant cell combusts fuel to radiantly heat the secondreformer effluent and the combusted fuel forms a second flue gas;introducing the second flue gas from the second radiant cell into theconvective bank so that the second flue gas mixes with the first fluegas to heat the naphtha feed stream; reacting the second reformereffluent in a third reformer reaction zone to form a third reformereffluent; heating the third reformer effluent in a third radiant cell,wherein the third radiant cell combusts fuel to heat the third reformereffluent and the combusted fuel forms a third flue gas; introducing thethird flue gas from the third radiant cell into the convective bank sothat the third flue gas mixes with the first flue gas to heat thenaphtha feed stream; and reacting the third reformer effluent in afourth reformer reaction zone to form a product effluent.
 17. The methodof claim 14 further comprising: passing the naphtha feed stream and theproduct effluent through a heat exchanger before heating the naphthafeed stream in the convective bank to preheat the naphtha feed stream.18. The method of claim 1 wherein the additional gas stream comprisesthe recycled portion of the exhaust gas, and further comprising:introducing the exhaust gas into a steam convection bank to producesteam and the recycled portion of the exhaust gas; and introducing therecycled portion of the exhaust gas into the convective bank.
 19. Themethod of claim 14 wherein the additional gas stream comprises therecycled portion of the exhaust gas, and further comprising: introducingthe exhaust gas into a steam convection bank to produce steam and therecycled portion of the exhaust gas; and introducing the recycledportion of the exhaust gas into the convective bank.